This proposal represents a renewal of an ongoing study, initiated in 1993, to evaluate the use of adenovirus (Ad) vectors to transfer and express the normal human cystic fibrosis transmembrane conductance regulator (CFTR) cDNA in the airway epithelium of individuals with cystic fibrosis (CF). The goal of these studies is to express the normal human CFTR cDNA in the airway epithelium of individuals with CF in sufficient amount, distribution, and persistence to compensate for the deficiency in normal CFTR gene expression that causes the respiratory manifestations of this disorder. Over the past 6 years, we have learned that: (1) Ad vectors are capable of transferring and expressing normal levels of CFTR mRNA in the airway epithelium of individuals with CF, but only transiently; and (2) although immune-mediated host defenses likely play a major role in limiting the duration of expression of Ad vector-mediated gene transfer following intrabronchial administration, the human studies suggest that human anti-Ad host defenses are more complex than those of animals. The hypothesis underlying the proposed studies is that by understanding the pulmonary host immune and inflammatory responses to local administration of replication deficient Ad vectors, a strategy can be developed to use a "stealth" Ad vector, combined with transient immunosuppression, to circumvent these host responses to enable Ad-mediated gene transfer to safely correct the biologic abnormalities of the airway epithelium of individuals with CF on a persistent basis. To evaluate this hypothesis, we propose to assess the persistence of the Ad vector genome, and the respiratory mucosal and systemic anti-Ad host defenses following intrabronchial administration of 2nd generation "stealth" Ad vectors (E4 or E3+), alone or together with transient systemic immunosuppression (corticosteroids or cyclosporine). Because the infected and inflamed respiratory epithelial surface in CF precludes evaluation of respiratory mucosal anti-Ad vector immune host defenses, we propose to carry out these studies in normal individuals, a study population in which we can investigate local (lung) anti-Ad responses to the Ad vectors in a fashion impossible in the CF population. The study will start with intrabronchial administration safety studies in normals with AdGVCD.10 (a 1st generation Ad vector that has already been administered by other routes to humans). Then, using airway epithelial vector genome persistence and anti-vector host responses to a 1st generation E1 E3 E4+ Null Ad vector as a baseline, the stealth Null vectors (E1 E3 E4 and E1 E3+ E4+) will be assessed alone, or with concomitant prednisone or cyclosporine administration. Should data be generated that demonstrate enhanced persistence of the Ad genome in the airway epithelium in normal individuals, the same vector design & immunosuppression will be used to evaluate the persistence of the vector genome, and CFTR expression following administration of an Ad vector containing normal human CFTR cDNA to individuals with CF.